Or, a triode-wired E810F/7788. Comparable in mu and gm to the 437A and 6C45, if not a tad more of each parameter. The 7721/D3a has a higher mu, but belongs in this "super tube" category too.

Also, although paralleling tubes has its own set of problems (and detractors) , two 417A/5842s in parallel is close to a 437A, at least in terms of specsmanship. Might be worth a try if you can achieve good current balance with two matched tubes.